1. Field of the Invention
This present application relates to lithium ion secondary batteries, and more particular, to a cap assembly for a lithium ion secondary battery.
2. Description of the Related Art
Lithium ion secondary batteries are widely used for high energy-density and rechargeable characters.
A typical lithium ion secondary battery includes a cap assembly 38 to be assembled to and enclose an upper end of a can 36. The cap assembly 38 includes a gasket 40, a cap cover 42, and a cap plate 52. The can 36 receives an electrode assembly and electrolyte. The gasket 40 receives the cap cover 42 and the cap plate 52. The cap cover 42 defines a number of through holes. The cap plate 52 is provided with a ring-shaped safety groove 54. When the internal pressure of the can 36 rises, the cap plate 52 will break along the safety groove 54 to evacuate gas to the exterior of the can 36 via the through hole of the cap cover 42. However, the electrolyte will also leak to the exterior via the through hole of the cap cover 42, which may result in burning and degradation of safety performance of the lithium secondary battery.
Therefore, it is desirable to provide a cap assembly for lithium ion secondary battery, which can overcome the problems and limitations as mentioned above.